Coil Structure and Heat Pump System Using the Same

ABSTRACT

The present invention relates to a coil structure, which provides a heating capacity not lower than a conventional heating capacity, reduces the work of a compressor, and executes double-stage condensation, and to a heat pump system which uses the coil structure and raises the temperature of heat as high as possible during condensation by executing first-stage compression and second-stage expansion. In the coil structure, a plurality of element tubes is connected to distribution conduits in parallel. When the coil is stood up, the element tubes are connected to each other in series to form five horizontal rows to one thousand horizontal rows of element tubes, and are connected to each other by the distribution conduits in parallel with each other to form a set of a single row or a set of two rows based on a vertical row.

TECHNICAL FIELD

The present invention relates, in general, to coil structures, which are configured to reduce the work of compressors, and to heat pump systems that use the coil structures and are capable of executing double-stage condensation and, more particularly, to a coil structure, which is configured to provide a heating capacity not lower than a conventional heating capacity, reduce the work of a compressor, and execute double-stage condensation, and to a heat pump system which uses the coil structure and raises the temperature of heat as high as possible during condensation by executing first-stage compression and second-stage expansion.

BACKGROUND ART

Generally, when a conventional heat pump system is operated in a heating mode to heat room air, the compressor of the system discharges refrigerant gas having a temperature higher than a condensation temperature. However, the heat of the hot refrigerant gas discharged from the compressor in the heating-mode operation of the conventional heat pump system is not efficiently used. Only heat of high temperature discharge air generated by the high condensation temperature is used.

Furthermore, the direction in which the refrigerant flows in the evaporator and the condenser is changed, so that the direction in which the refrigerant flows along a coil is changed to the opposite direction.

To overcome the above-mentioned problems, several techniques in which the coil structure of an evaporator or a condenser is constructed such that the flow direction of refrigerant is opposite the flow direction of air were proposed in Japan Patent Laid-open Publication No. Hei. 7-091761, Japan Patent Laid-open Publication No. Hei. 1-139960, Japan Patent Laid-open Publication No. Hei. 6-129732, Japan Patent Laid-open Publication No. Hei. 11-230637, Japan Patent Laid-open Publication No. Hei. 7-280375, Korean Patent Laid-open Publication No. 1999-029909 and Korean Patent Laid-open Publication No. 2001-0024437.

FIGS. 1A through 1C schematically illustrate the structure of a conventional coil and a cooling-mode operation and a heating-mode operation of the coil, respectively.

As shown in FIG. 1A, the element tubes of the conventional coil are arranged in vertical directions relative to the flow direction of air and are connected to each other in a series arrangement (this arrangement of the element tubes may be called “series-vertical type element tube arrangement”). In the conventional coil structure, refrigerant flows upwards or downwards in the element tubes.

In the description of the arrangement of the element tubes of the coil, the terms “horizontal” and “vertical” are defined in the context of the concept of direction relative to the direction of gravity and the flow direction of air.

Further, the terms “vertical”, “horizontal”, “upper” and “lower” concerned with the flow directions of air and refrigerant are also defined in the context of the concept of direction relative to the direction of gravity.

Further, the term “coil” in the description is defined as the structure comprising a main conduit, a distribution conduit diverging from the main conduit, and a plurality of element tubes connected to each other by the distribution conduit.

Further, the element tubes of a conventional condenser coil are configured as a reversed U-shape, a II-shape, a V-shape, or an I-shape. In the related art, the element tubes having the reversed U-shape or I-shape are made of single pipes, while the element tubes having the II-shape or V-shape are configured as two sets of pipes. The conventional evaporator coils are configured as single pipes regardless of the evaporation capacity. If the conventional evaporator coils are used in a ceiling cassette-type evaporator unit or a specific-type evaporator unit, which divides the flow direction of air into several directions, one set of element tubes is provided for each area corresponding to one air passing direction.

To increase the capacity of coils, the conventional technique configures the evaporator or condenser coil as two, three or four rows of element tubes arranged horizontally according to the capacity thereof. The capacity of the coils may be further increased by increasing the number of vertical element tubes in each of the two, three or four rows of horizontal coils. In the related art, respective lines distributed from a main conduit are configured as two, three or four rows of element tubes arranged horizontally and as four or more rows of element tubes arranged vertically by making the vertical length of the coil structure longer than the horizontal length. When the element tubes, having thin walls and a multiple-row structure in a vertical direction, are stood up longitudinally, the refrigerant flows vertically upwards or downwards along the element tubes. Furthermore, while the refrigerant flows vertically as described above, air flows horizontally outside the element tubes, so that the air and refrigerant can exchange heat while crossing each other in a cross flow state. To meet the requirement for increased capacity, the element tubes are distributed by distribution conduits to form a multi-tiered structure, so that four or more rows of element tubes are provided in a vertical arrangement. In the case of a coil used as an evaporator, the refrigerant exchanges heat with air through an endothermic reaction using latent heat of vaporization, so that the temperature of the upper end of the coil is very similar to the temperature of the lower end of the coil. Thus, the temperature of air passing through the coil used as an evaporator can be kept constant, while the temperature of air passing through the coil used as a condenser is easily varied.

As described above, the temperature of the compressor discharge gas is significantly higher than the condensation temperature and, furthermore, the quantity of heat within a superheated vapor section from the exhaust to condensation temperature is equal to about 20% of condenser heat. Thus, the temperature of air passing through the condenser coil reaches the condensation temperature while passing both a part directly affected by heat of high temperature exhaust gas and the superheated vapor section, thus being different from the temperature of air which dissipates heat as latent heat without being changed in the temperature thereof. Therefore, the temperature of air passing the coil in a superheated vapor state is higher than the condensation temperature, while the temperature of air passing the coil in a latent heat state is lower than the condensation temperature, so that the higher temperature air is mixed with lower temperature air, resulting in exhaust air having an intermediate temperature.

Therefore, the conventional technique is problematic in that, although the temperature of compressor discharge gas is higher than the condensation temperature, the refrigerant in the element tubes according to the conventional technique flows vertically, while air outside the element tubes flows horizontally. Thus, the conventional technique cannot increase the temperature of the heat pump discharge air to a level higher than the condensation temperature, thereby increasing the work of the compressor, reducing condenser heat, and reducing the refrigeration capacity.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a coil structure, which reduces the work of a compressor and executes double-stage condensation, and a heat pump system, which uses the coil structure to raise the temperature of heat as high as possible during condensation by executing first-stage compression and second-stage expansion.

Technical Solution

In order to accomplish the above object, the present invention provides a direct expansion-type coil structure, which is configured such that refrigerant flowing in a coil and air flowing outside an external surface of the coil exchange heat while the refrigerant and air flow in opposite directions to form opposing currents, the coil structure comprising: a plurality of element tubes configured such that refrigerant inlets of the element tubes are connected to a distribution conduit in parallel with each other when the coil is stood up, and refrigerant outlets of the element tubes are joined together in parallel with each other at another distribution conduit prior to being led outside the coil, wherein when the coil is stood up, the element tubes are connected to each other in series to form five horizontal rows to one thousand horizontal rows of element tubes; and the element tubes are connected to each other by the distribution conduits in parallel with each other to form a set of one row or a set of two rows based on a vertical row.

In another aspect, the present invention provides a direct expansion-type coil structure, which is configured such that refrigerant flowing in a coil and air flowing outside an external surface of the coil exchange heat while the refrigerant and air flow in opposite directions to form opposing currents, the coil structure comprising: a plurality of element tubes divided into vertical sets and connected to distribution conduits such that, when the coil is stood up vertically, the element tubes form a set of two vertical rows, which couples the distribution conduits in parallel with each other and causes refrigerant to repeatedly flow horizontally through the element tubes between a first vertical row and a second vertical row.

In addition, an expansion valve may be provided at a predetermined position of an outflow main conduit of the element tubes, thus executing double-stage condensation.

In a further aspect, the present invention provides a heat pump system comprising an evaporator, a compressor, a condenser and an expansion valve, wherein the evaporator and the condenser have the above-mentioned coil structure.

Further, in the heat pump system, an expansion valve may be provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil may expand under reduced pressure at a temperature higher than a room inlet, so that the heat pump can utilize double-stage condensation.

ADVANTAGEOUS EFFECTS

The present invention provides the following advantages.

First, the present invention provides a coil structure for indoor and outdoor units, which is configured such that a plurality of element tubes is arranged in a spaced and multi-tiered arrangement. Thus, the present invention increases the heat exchanging efficiency of the coil structure and provides a desired heat exchange capacity while reducing the production costs of the coil structure. When the coil structure of the present invention is configured using the same number of element tubes as that of a conventional coil structure, the coil used as an evaporator coil can increase evaporation pressure due to an increase in the heat exchanging efficiency. Furthermore, the coil of the present invention used as a condenser coil reduces condensation pressure, so that the compressive ratio can be reduced, but the refrigeration capacity and condensation capacity can be increased. Thus, the coil of the present invention, used as a condenser coil, can realize higher capacities than conventional coils using the same amount of energy. Therefore, the coil reduces the amount of energy consumed and satisfies the recent trend of increased operational efficiency, superior conservation of electricity and reduced energy consumption.

Second, unlike a conventional coil structure for indoor or outdoor units, in which the coil is configured as a single set of element tubes arranged in the direction of air flow, the present invention configures the coil such that the element tubes are optimally divided vertically to form opposing currents of air and refrigerant. Thus, the coil of the present invention, used as a condenser coil, optimally takes advantage of the fact that the temperature within a superheated vapor section is higher than the condensation temperature. The temperature of air passing outside the external surface of the coil is increased by optimally using the high temperature of discharge gas. Therefore, during a heating-mode operation, the present invention can generate air having a temperature higher than that of a conventional technique or air having the same temperature as that of the conventional technique, at a lower condensation pressure. Because the present invention provides an exhaust air temperature lower than that of the conventional technique at a lower condensation pressure, the present invention reduces the compressive ratio, thus reducing the amount of electric power consumed and satisfying the recent trend of increased operational efficiency, superior conservation of electricity and reduced energy consumption.

Third, unlike a conventional coil structure, which is used for heating while executing single-stage condensation, the coil structure of the present invention is used for primary heating while executing first-stage condensation in the same manner as the conventional technique and is, thereafter, reused for secondary heating while executing second-stage expansion of refrigerant under reduced pressure at a temperature lower than the temperature of a heat medium flowing outside the external surfaces of the element tubes, thus improving the condensation capacity in comparison with the conventional coil structure.

DESCRIPTION OF DRAWINGS

FIGS. 1A through 1C schematically illustrate the structure of a conventional element tube of a coil, which illustrates the flow direction of refrigerant relative to the flow direction of air, a cooling-mode operation of a coil using the element tubes, and a heating-mode operation of the coil, respectively;

FIGS. 2A through 2F are views illustrating the aspects of coils related to the flow direction of refrigerant relative to the flow direction of air in coil structures according to the present invention, in which

FIGS. 2A and 2B are a perspective view and a front view illustrating coils, in which the element tubes are arranged in oblique directions and in horizontal directions relative to the flow direction of air;

FIGS. 2C and 2D are views illustrating coils, in which the element tubes are arranged in oblique directions relative to the flow direction of air; and

FIGS. 2E and 2F are a perspective view and a front view illustrating the appearance of the coils of FIGS. 2A through 2D;

FIG. 3 is a view schematically illustrating the element tubes of a coil according to the present invention, which are divided with respect to the flow direction of air;

FIG. 4 is a diagram schematically illustrating a cooling-mode operation of a heat pump system according to the present invention; and

FIG. 5 is a diagram schematically illustrating a heating-mode operation (conversion of function of an outdoor unit) of the heat pump system according to the present invention.

DESCRIPTION OF THE ELEMENTS IN THE DRAWING

-   -   11: compressor     -   12: outdoor unit coil     -   13: cooling expansion valve     -   14: indoor unit coil     -   15: indoor unit fan     -   16: outdoor unit fan     -   17: refrigerant conduit (liquid conduit in cooling mode)     -   18: refrigerant conduit (gas conduit in cooling mode)     -   19: heating expansion valve     -   20: three way exhaust valve     -   21: three way suction valve     -   22, 29, 35, 36, 38, 39: electronic valve     -   23, 24, 25, 26, 27, 30, 31: conduit     -   28: three way indoor unit valve     -   32: indoor unit     -   33: outdoor unit     -   40: element tube     -   42: distribution conduit     -   44: inflow main conduit     -   46: outflow main conduit

BEST MODE

Hereinafter, preferred embodiments of coil structures and heat pump systems using the coil structures according to the present invention will be described in detail with reference to the accompanying drawings, FIGS. 2A through 5.

FIGS. 2A through 2F are views illustrating the flow directions of refrigerant and air in the coil structures according to the present invention. FIG. 3 is a view schematically illustrating the element tubes of a coil according to the present invention, which is divided with respect to the flow direction of air. FIG. 4 is a diagram schematically illustrating the cooling-mode operation of a heat pump system according to the present invention. FIG. 5 is a diagram schematically illustrating the heating-mode operation (conversion of function at an outdoor unit) of the heat pump system according to the present invention.

Described in detail, FIGS. 2A and 2B are a perspective view and a front view illustrating coils, in which the element tubes 40 are arranged in oblique directions and in horizontal directions relative to the flow direction of air, thus forming a single row in series and making refrigerant flow in the opposite direction as air.

FIGS. 2C and 2D are views illustrating coils, in which the element tubes 40 are arranged in oblique directions relative to the flow direction of air, thus forming a multi-tiered structure, and diverge from a distribution conduit 42.

FIGS. 2E and 2F are a perspective view and a front view illustrating the appearance of the coils of FIGS. 2A through 2D.

Furthermore, in a conventional coil structure, the refrigerant and air flow as follows. When the element tubes, used in an indoor unit coil, are stood up vertically, the conventional technique is to arrange the element tubes in a parallel arrangement, in which two rows of element tubes may be arranged horizontally to provide a small capacity, or two to four rows of element tubes may be arranged horizontally to provide a large capacity and, furthermore, about five rows of element tubes may be arranged vertically to provide an appropriate capacity, thus forming one set of element tubes. Several sets of element tubes in the conventional coil structure are distributed from a distribution conduit to form a parallel arrangement or a multi-tiered arrangement. Thus, the refrigerant may sequentially flow upwards or downwards through the element tubes arranged in the multi-tiered arrangement. However, when the element tubes 40 of the present invention, used in an indoor unit coil, are stood up vertically as shown in 2C, the element tubes 40 are arranged such that four or more rows of element tubes are arranged horizontally. In the coil structure of the present invention, the refrigerant flows through the element tubes and is guided to neighboring element tubes such that the refrigerant passes from a first row of horizontal element tubes and a first row of vertical element tubes to a second row of horizontal element tubes and the first row of vertical element tubes, and thereafter, from a third row of horizontal element tubes and the first row of vertical element tubes to a fourth row of horizontal element tubes and the first row of vertical element tubes. In a brief description, the refrigerant flows horizontally from the first row of vertical element tubes. Furthermore, the number of element tube rows may be increased to satisfy the desired capacity of the element tubes, and a distribution conduit 42 may be coupled to each vertical row of element tubes, so that the vertical rows of element tubes are fed from the distribution conduit 42 in parallel with each other. When the coil of the present invention is used as a condenser coil, the element tubes have different temperatures such that the first row of horizontal element tubes has the highest temperature and the temperature of the element tubes is gradually reduced in order from the second row of horizontal element tubes through the third row of horizontal element tubes. The refrigerant passes through the superheated vapor section and reaches a condensation temperature in a wet vapor section and, thereafter, is condensed and liquidized, prior to being supercooled in the supercooling section.

FIG. 2D illustrates the element tubes 40, which are arranged obliquely according to another embodiment of the present invention. In this embodiment, the refrigerant and air flow in opposite directions to form opposing currents in the same manner as that described for the embodiments of FIGS. 2A and 2B.

In a conventional coil structure, when the element tubes are arranged in the

-direction, the refrigerant may flow in the

-direction or in the

-direction. The

-direction is opposite to the direction of the element tubes. Described in brief, the direction of the element tubes and the flow direction of the refrigerant in the conventional coil structure may be set such that the element tubes are arranged in the

-direction and the refrigerant flows in the same

-direction, or the element tubes are arranged in the

-direction and the refrigerant flows in the

-direction, opposite to the direction of the element tubes. Thus, the direction of the element tubes may be opposite to the flow direction of the refrigerant, thus causing the refrigerant to flow in the form of opposing current. Alternatively, the element tubes may be arranged in the same direction as the flow direction of the refrigerant, thus causing the refrigerant to flow in the form of forward current.

However, when the element tubes 40 of the present invention are arranged obliquely, as shown in FIG. 2D, the refrigerant may flow along paths which cross the element tubes 40 to form X-shaped crosses. However, when the element tubes of the present invention are arranged obliquely in the

-direction and air flows outside the element tubes in the ↑-direction, the refrigerant may flow in the ↓-direction to cause the air and refrigerant to flow in opposite directions. Furthermore, the refrigerant may flow in the

-direction such that the element tubes are arranged in the

-direction and the refrigerant flows in the ↓-direction, or the element tubes are arranged in the

-direction and the refrigerant flows in the

-direction so that the air and refrigerant flow in opposite directions such that air flows in the ↑-direction and refrigerant flows in the ↓-direction. Furthermore, the refrigerant may flow in the

-direction and air may flow in the ↑-direction, so that the leading part of the air exchanges heat with the trailing part of the refrigerant, which passes through the element tubes. During a heating-mode operation of the coil, the temperature of air flowing outside the element tubes is higher than the temperature of refrigerant flowing through the element tubes, so that air exchanges heat with the refrigerant and the temperature of the air may increase as the air passes through the coil. In the present invention, when the element tubes are arranged obliquely in the

-direction and the air outside the element tubes flows in the ‘←’-direction, the refrigerant flows in the ‘→’-direction, so that the air and refrigerant flow in opposite directions to form opposing currents. Described in brief, the refrigerant flows in the ‘→’-direction, while the air flows in the ‘←’-direction, so that opposing currents of air and refrigerant are generated. Furthermore, if the element tubes are arranged in the

-direction and air flows in the ‘←’-direction, the refrigerant flows in the

-direction, opposite the direction of the element tubes. Described in brief, the refrigerant flows in the direction opposite the flow direction of air, so that the air and refrigerant form opposing currents.

FIG. 3 illustrates a further embodiment of the present invention, in which each set of element tubes is formed by two vertical rows of element tubes, unlike FIGS. 2A and 2D. If each set of element tubes is formed by two vertical rows of element tubes, the refrigerant flows from an inflow main conduit 44 to the distribution conduit 42 and is, thereafter, distributed from the distribution conduit 42 to the element tubes 40, which are coupled to the distribution conduit 42 in parallel with each other. Thus, the refrigerant repeatedly flows through the two rows of vertical element tubes, so that the flow direction of refrigerant is opposite to the flow direction of air, forming opposing currents. Thereafter, the refrigerant from the two rows of vertical element tubes is discharged from the coil structure through an outflow main conduit 46.

In the present invention, the embodiments of FIGS. 2B, 2C and 2D have different patterns of element tubes. However, the flow directions of refrigerant do not change regardless of whether the operation is a cooling-mode operation or a heating-mode operation, but the air and refrigerant always flow in opposite directions to form opposing currents, unlike the conventional technique.

FIGS. 2E and 2F are views illustrating the appearance of the coil structure of FIGS. 2A through 2D. As shown in the drawings, the coil of the present invention comprises an inflow main conduit 44 and two or more distribution conduits 42 coupled to the lower part of the inflow main conduit 44. Thus, refrigerant, which has been introduced into the coil through the inflow main conduit 44, is primarily distributed from the distribution conduit 42 at point C and flows into the element tubes 40, so that air and refrigerant flow in opposite directions to form opposing currents and exchange heat with each other. In the above state, the refrigerant, which forms opposing current, flows through the element tubes 40 horizontally, obliquely or vertically while exchanging heat with air through the element tubes. The element tubes are arranged to form a set of a single row of element tubes or a set of two rows of element tubes, and are joined together at an outlet side distribution conduit 42 a. Thereafter, two or more sets of distribution conduits are joined together at the outflow main conduit 46, thus discharging the refrigerant outside the coil.

FIG. 3 is a view schematically illustrating the element tubes of a coil according to the present invention, which are divided with respect to the flow direction of air. The coil of the present invention is configured such that the I-shaped element tubes are also divided vertically to form two or more sets of element tubes. The I-shaped element tubes have a rectangular shape when viewed from the flow direction of air.

Furthermore, unlike the conventional technique, in which the rectangular element tubes have been configured as a single set of element tubes, the present invention vertically divides the rectangular element tubes to form two or more sets of element tubes. That is, the present invention can divide the element tubes into three sets, four sets or more sets of element tubes according to the desired increase in capacity.

However, unlike the conventional technique, in which a single set of element tubes is provided for each area corresponding to one air passing direction, the present invention vertically divides the horizontal element tubes to reduce the length of each horizontal element tube and provides two or more sets of element tubes for each area corresponding to one air passing direction to satisfy the requirement for a large capacity. When a small capacity coil is required, the element tubes of the present invention may be configured as a single set of element tubes to be used in a limited space. However, it is preferred that the coil structure of the present invention be configured such that the element tubes are divided if space allows.

Thus, in the present invention, the element tubes are preferably divided into two or more sets of vertically arranged element tubes for each unit area corresponding to one air passing direction.

If the coil of the present invention is used in an indoor unit, the coil executes a cooling-mode operation at uniform pressure inside the element tubes. However, during a heating-mode operation, it is preferred that the element tubes be divided into two or more sets to execute double or multi-stage condensation.

To configure the coil such that the coil executes double-stage condensation, the element tubes, which are arranged to form currents of refrigerant opposite air, have a parallel structure distributed in one row or two rows of horizontal element tubes in a vertical structure such that several lines of horizontal or oblique element tubes are coupled together in the flow direction of air, thus forming one set of element tubes. When the set of element tubes comprises six or more rows of element tubes, the set of element tubes is divided into two parts, each of which comprises three rows of element tubes. The divided rows of element tubes are joined together into a conduit after passing through each set of lines, and an electronic expansion valve (or another expansion valve having an equivalent function) is attached to the joined conduit. The element tubes are subsequently distributed by a distribution conduit to front and rear sets of element tubes such that the front and rear sets of element tubes have different pressures.

The front set of element tubes executes a condensation process in a general heating cycle. In the rear set of element tubes, the pressure of the refrigerant is reduced by the expansion valve provided on the intermediate portion of the coil, so that the temperature of the refrigerant is regulated through double-stage condensation to become lower than the first-stage condensation temperature and higher than the temperature of indoor unit suction air. The refrigerant in the rear set of element tubes preheats the indoor unit suction air. Thereafter, the refrigerant in the front set of element tubes heats indoor unit discharge air using both the first-stage condensation temperature and hot exhaust gas, thus increasing the temperature of the indoor unit discharge air to a level higher than the first-stage condensation temperature.

FIG. 4 is a diagram schematically illustrating refrigerant flow in a cooling cycle of a heat pump system of the present invention. As shown in FIG. 4, in the cooling cycle, refrigerant gas discharged from a compressor 11 flows into an outdoor unit coil 12 through a conduit 26. While the refrigerant gas flows through the outdoor unit coil 12, the refrigerant gas is cooled by outdoor air drawn to the coil 12 by an outdoor unit fan 16, so that the refrigerant gas condenses and becomes liquidized. Thereafter, the refrigerant passes through an open electronic valve 22, thus flowing from an outdoor unit 33 to an indoor unit 32 through a refrigerant conduit 17. In the indoor unit 32, the refrigerant is throttled and expands in a cooling expansion valve 13, so that the pressure of the refrigerant is reduced. While the refrigerant under low pressure passes through an indoor unit coil 14, the refrigerant exchanges heat with room air drawn into the indoor unit 32 by an indoor unit fan 15, so that the refrigerant evaporates to thus enter a vapor phase. The vaporized refrigerant flows from the indoor unit 32 to the outdoor unit 33 through a refrigerant conduit 18 and is drawn into the compressor 11, in which the vaporized refrigerant is compressed, prior to repeating the above-mentioned cycle. During the cooling-mode operation, the refrigerant circulates through the above-mentioned cycle to absorb heat from room air and dissipate heat to outdoor air. In the above state, a heating expansion valve 19 is closed, a three way exhaust valve 20 closes a conduit 23, a three way suction valve 21 closes another conduit 25, and the electronic valve 22 is opened, so that the refrigerant can repeatedly circulate through the following cooling cycle.

Compressor 11→outdoor unit coil 12→refrigerant conduit 17→cooling expansion valve 13→indoor unit coil 14→refrigerant conduit 18→compressor 11

FIG. 5 is a diagram schematically illustrating refrigerant flow in a heating cycle of the heat pump system of the present invention. As shown in FIG. 5, the refrigerant gas, discharged from the compressor 11 during a heating-mode operation, flows from the outdoor unit 33 to the indoor unit 32 through the conduit 23 and the refrigerant conduit 17, because the three way exhaust valve 20 closes the conduit 26 (acting as an outflow main conduit during a cooling-mode operation), and opens the conduit 23 (acting as an outflow main conduit during a heating-mode operation). In the above case, the electronic valve 22 is closed, so that the refrigerant gas does not flow into the outdoor unit coil. The refrigerant, which flows in the indoor unit 32 through the refrigerant conduit 17, exchanges heat with room air, which is drawn to the indoor unit coil 14 by the indoor unit fan 15. Thus, the refrigerant dissipates heat to the room air, condenses, and becomes liquidized, so that the refrigerant executes a heating-mode operation. Thereafter, the refrigerant flows from the indoor unit 32 to the outdoor unit 33 through the refrigerant conduit 18. In the outdoor unit 33, the refrigerant flows to the heating expansion valve 19 through the conduit 24 (acting as a liquid conduit during a heating-mode operation), thus throttle-expanding in the valve 19. Thereafter, the refrigerant flows through the outdoor unit coil 12 and absorbs heat from outdoor air, which is drawn to the coil 12 by the outdoor unit fan 16, so that the refrigerant evaporates to become vaporized refrigerant. The vaporized refrigerant flows to the three way suction valve 21 through the conduit 25 (acting as an inflow main conduit during a heating-mode operation), and is drawn into the compressor 11, in which the vaporized refrigerant is compressed, prior to repeating the above-mentioned cycle. During the heating-mode operation, the refrigerant circulates through the above-mentioned cycle to absorb heat from outdoor air and dissipate heat to room air. In the above state, the heating expansion valve 19 is opened, the cooling expansion valve 13 is fully opened, the three way exhaust valve 20 closes the conduit 26 and opens the conduit 23, the three way suction valve 21 closes the conduit 27 and opens the conduit 25, and the electronic valve 22 is closed, so that the refrigerant can repeatedly circulate through the following heating cycle.

Compressor 11→refrigerant conduit 17→indoor unit coil 14→refrigerant conduit 18→heating expansion valve 19→outdoor unit coil 12→compressor 11

EMBODIMENTS 1. First Embodiment Condensation Pressure in the Case of Using the Coil Structure of the Present Invention

In the above-mentioned coil structure, the element tubes are divided vertically to form vertical sets of element tubes. The element tubes are connected to distribution conduits in parallel with each other such that, when the coil structure is stood up vertically, the element tubes form a set of two rows, which couples the distribution conduits to each other and causes refrigerant to repeatedly flow horizontally through the element tubes between a first vertical row and a second vertical row. The condensation temperature of the coil structure according to the present invention is compared to the condensation temperature of a conventional coil structure, in which the refrigerant in the element tubes and air outside the element tubes flow in opposite directions to form opposing currents while exchanging heat with each other, and the results of comparison are given in Table 1. TABLE 1 Exhaust gas Condensation Condensation Exhaust air tempera- tempera- pressure temperature ture ° C. ture ° C. (Kg/cm2 abs.) ° C. Related 82 57 23 45 art Present 70 40 15.8 45 invention

In the conventional technique, air passing through the condenser has different temperatures according to whether the coil of the condenser, around which the air passes and through which refrigerant passes, is in a superheated vapor section, a wet vapor section or a supercooled section, and the different temperatures of air are mixed with each other to form an intermediate temperature. Thus, a heat pump of the conventional technique may execute a heating-mode operation such that it produces an exhaust air temperature that is lower than the condensation temperature, so that, to produce a high exhaust air temperature during the heating-mode operation, the condensation pressure is increased to increase the condensation temperature. However, the present invention vertically divides the element tube structure so that it can optimally utilize the temperature of the superheated vapor section, which is higher that the condensation temperature. Air passing through the coil structure of the present invention has a constant temperature distribution regardless of which parts of the coil the air passes through, thus producing an exhaust air temperature higher than the condensation temperature. Therefore, the present invention notably provides lower condensation pressure in comparison with the conventional technique, as illustrated in the Table 1.

Furthermore, when the heat pump system of the present invention is operated in a heating mode, the outdoor unit coil functions as an evaporator. In the above state, the system of the present invention can increase the amount of heat exchanged between the refrigerant and air in the case of a coil made using the same number of element tubes as the conventional technique. Thus, even if the temperature of outdoor air is reduced to a low level, the evaporation temperature preferably approaches the outdoor air temperature, to thus become higher than in the conventional technique. Therefore, the power consumed by the compressor due to the evaporation pressure is reduced and, furthermore, the specific volume of drawn vapor is reduced in comparison with the conventional technique. Thus, the evaporation temperature in the conventional technique is reduced, so that the quantity of refrigerant circulated is reduced and the refrigeration capacity and heating capacity are reduced. Unlike the conventional technique, the present invention preferably reduces the quantity of frost deposited on the outdoor unit coil and saves the time required to defrost the outdoor unit coil, thus executing a stable heating-mode operation in comparison with the conventional technique.

Therefore, it is noted that, when the coil of the present invention is adapted to a heating-mode operation, the coil remarkably and desirably reduces condensation pressure in comparison with the coil according to the conventional technique.

2. Second Embodiment Condensation Pressure in the Case of Using the Coil Structure of the Present Invention and an Expansion Valve Provided in an Intermediate Portion of the Coil

The inventor of the present invention compared the condensation capacity of a conventional system, which is used in a heating-mode operation while executing single-stage condensation, to the condensation capacity of the system according to the present invention, which is configured such that the system is used in a heating-mode operation while executing double or multi-stage condensation by expanding the refrigerant under reduced pressure at a temperature lower than the temperature of a heat medium flowing outside the external surfaces of the element tubes. The comparison results are given in the Table 2. TABLE 2 Exhaust exhaust expansion valve air condensation gas inlet enthalpy temperature tempera- enthalpy (evaporator side (evaporator ture° C. (kcal/kg) kcal/kg) side ° C.) conventional 57 162 115 45 technique The 57 162 102 45 present invention

Condensation capacity=exhaust gas enthalpy−expansion valve inlet enthalpy (evaporator side)

The condensation capacity of the conventional system per kg refrigerant is 47 kcal/h (162 kcal/h−115 kcal/h). However, the present invention provides a condensation capacity of 60 kcal/h (162 kcal/h−102 kcal/h), so that the condensation capacity of the present invention increases by 13 kcal/h in comparison with the conventional technique. Therefore, it is noted that the condensation capacity of the present invention increases by 27.7%.

In the above description of the preferred embodiments, the present invention is adapted to heating systems. However, it should be understood that the present invention may be adapted to a secondary refrigerant coil of a heat pump system, which uses brine (water or antifreeze liquid) as secondary refrigerant. In the above case, the present invention increases the difference between the inlet temperature and the outlet temperature more than does the conventional technique. 

1. A direct expansion-type coil structure, which is configured such that refrigerant flowing in a coil and air flowing outside an external surface of the coil exchange heat while the refrigerant and air flow in opposite directions to form opposing currents, the coil structure comprising: a plurality of element tubes configured such that refrigerant inlets of the element tubes are connected to a distribution conduit in parallel with each other when the coil is stood up, and refrigerant outlets of the element tubes are joined together in parallel with each other at another distribution conduit prior to being led outside the coil, wherein when the coil is stood up, the element tubes are connected to each other in series to form five horizontal rows to one thousand horizontal rows of element tubes; and the element tubes are connected to each other by the distribution conduits in parallel with each other to form a set of one row or a set of two rows based on a vertical row.
 2. A direct expansion-type coil structure, which is configured such that refrigerant flowing in a coil and air flowing outside an external surface of the coil exchange heat while the refrigerant and air flow in opposite directions to form opposing currents, the coil structure comprising: a plurality of element tubes divided into vertical sets and connected to distribution conduits such that, when the coil is stood up vertically, the element tubes form a set of two vertical rows, which couples the distribution conduits in parallel with each other and causes refrigerant to repeatedly flow horizontally through the element tubes between a first vertical row and a second vertical row.
 3. The coil structure according to claim 1, further comprising: an expansion valve provided at a predetermined position of an outflow main conduit of the element tubes, thus executing double-stage condensation.
 4. The coil structure according to claim 2, further comprising: an expansion valve provided at a predetermined position of an outflow main conduit of the element tubes, thus executing double-stage condensation.
 5. A heat pump system comprising an evaporator, a compressor, a condenser and an expansion valve, wherein the evaporator and the condenser have a coil structure according to any one of claims
 1. 6. A heat pump system comprising an evaporator, a compressor, a condenser and an expansion valve, wherein the evaporator and the condenser have a coil structure according to any one of claims
 2. 7. A heat pump system comprising an evaporator, a compressor, a condenser and an expansion valve, wherein the evaporator and the condenser have a coil structure according to any one of claims
 3. 8. A heat pump system comprising an evaporator, a compressor, a condenser and an expansion valve, wherein the evaporator and the condenser have a coil structure according to any one of claims
 4. 9. The heat pump system according to claim 4, further comprising: an expansion valve provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil expands under reduced pressure at a temperature higher than a room inlet, so that the heat pump utilizes double-stage condensation.
 10. The heat pump system according to claim 5, further comprising: an expansion valve provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil expands under reduced pressure at a temperature higher than a room inlet, so that the heat pump utilizes double-stage condensation.
 11. The heat pump system according to claim 6, further comprising: an expansion valve provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil expands under reduced pressure at a temperature higher than a room inlet, so that the heat pump utilizes double-stage condensation.
 12. The heat pump system according to claim 7, further comprising: an expansion valve provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil expands under reduced pressure at a temperature higher than a room inlet, so that the heat pump utilizes double-stage condensation.
 13. The heat pump system according to claim 8, further comprising: an expansion valve provided in an intermediate portion of the coil, thus executing double-stage condensation, wherein, during heating-mode operation of the coil, air flowing outside the external surface of the coil expands under reduced pressure at a temperature higher than a room inlet, so that the heat pump utilizes double-stage condensation. 